An organic light emission phenomenon is one of the examples of converting current into visible rays through an internal process of a specific organic molecule. The principle of the organic light emission phenomenon is as follows.
When an organic material layer is disposed between a positive electrode and a negative electrode, if voltage is applied between the two electrodes, electrons and holes are injected from the negative electrode and the positive electrode, respectively, into the organic material layer. The electrons and the holes which are injected into the organic material layer are recombined to form an exciton, and the exciton falls down again to the ground state to emit light. An organic light emitting diode using this principle may be composed of a negative electrode, a positive electrode, and an organic material layer disposed therebetween, for example, an organic material layer including a hole injection layer, a hole transporting layer, a light emitting layer, and an electron transporting layer.
The materials used in the organic light emitting diode are mostly pure organic materials or complex compounds in which organic materials and metals form a complex, and may be classified into a hole injection material, a hole transporting material, a light emitting material, an electron transporting material, an electron injection material, and the like according to the use thereof. Here, an organic material having a p-type property, that is, an organic material, which is easily oxidized and electrochemically stable when the material is oxidized, is usually used as the hole injection material or the hole transporting material. Meanwhile, an organic material having an n-type property, that is, an organic material, which is easily reduced and electrochemically stable when the material is reduced, is usually used as the electron injection material or the electron transporting material. As the light emitting layer material, a material having both p-type and n-type properties, that is, a material, which is stable during both the oxidation and reduction states, is preferred, and when an exciton is formed, a material having high light emitting efficiency for converting the exciton into light is preferred. There is a need for developing an organic light emitting diode having high efficiency in the art.